/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.inlong.sort.formats.metrics.gauge;

import org.apache.flink.metrics.Gauge;

/**
 * Gauge metric for event time lag.
 */
public class EventTimeDelayGauge implements Gauge<Long> {

    private Gauge gauge;
    private long previousValue;
    private long currentValue;

    public synchronized void gauge(long gaugeValue) {
        this.currentValue = gaugeValue;
    }

    private synchronized Long gauge() {
        if (currentValue == previousValue) {
            return null;
        } else {
            previousValue = currentValue;
            return currentValue;
        }
    }

    @Override
    public Long getValue() {
        return gauge();
    }
}
